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​This is still one of the most common questions I hear from my clients. Both men and women have concerns about the phytoestrogens in soy so I wanted to share some of the science and research on the topic, and hopefully help ease some of those concerns.

First it is important to point out –– there is no mammalian estrogen in soy.

The plant-estrogens (phytoestrogens) in soy do not act the same way as mammalian estrogen. This is due to the differences in structure, and the type of estrogen receptors that they prefer to interact with.

There are two types of estrogen receptors in the body, ERalpha and ERbeta. Phytoestrogens from soy prefer to bind to ERbeta receptors which actually help reduce the effects of stronger estrogens in the body, including the estrogen-mimicking chemicals (also known as xenoestrogens) found in plastics, pesticides, personal care products, cleaning products, and cologne to name a few.

One of the ways that phytoestrogens have this protective effect is by physically blocking the stronger estrogens from binding to the receptors.

Mammalian estrogen and xenoestrogens always have a strong estrogenic effect. In contrast, phytoestrogens can have an weak estrogenic, anti-estrogenic, or neutral effect. Phytoestrogens are therefore classified as SERMS (selective estrogen receptor modulators).

Phytoestrogens also decrease the risk of breast cancer and prostate cancer. We wouldn't see this effect if phytoestrogens acted like mammalian estrogen. When the ERalpha receptors in the breast tissue are activated by regular estrogen it stimulates cell proliferation (i.e. increasing breast cancer risk). When ERbeta receptors in the breast tissue are activated by phytoestrogen it blocks the proliferative effects. This is another mechanism for how phytoestrogens have a protective effect.

This brings us to the hormonal effects of animal products. There is actual estrogen in breast milk from mammals. Dairy is a very hormonal fluid since it is designed to support rapid growth in baby animals. There are also traces of real estrogen in all meat since it is a hormone produced by the animal.

In addition to the naturally present hormones in animal products, the environmental estrogens end up accumulating in animal products because they are fat-soluable. So not only are you getting mammalian estrogen, you also get all those estrogen-mimicking chemicals. Check out this research linking fish intake to lower testosterone levels.

There have been two case studies (1, 2) linking soy intake with negative hormonal outcomes in men but these men were consuming 12+ servings a day. I think consuming anything in that amount would lead to some sort of imbalance. To compare, I would like to see what the effects would have been if these men were drinking that much cows milk.

There are no issues with men consuming an average amount of soy (3-5 servings a week). Even up to 1 serving a day should not impact hormone levels. Generally, I recommend no more than 1 serving every 1-3 days, not because of hormonal issues but to help increase the variety of other plant-foods in the diet. It can be easy for vegans to overly rely on soy products but doing so will cut down on the amounts of other beans, legumes, nuts, and seeds needed for a well-balanced diet.

With all that being said, you can definitely be vegan and not consume soy products if you don't want to, there is just no reason not to occasionally enjoy some as long as you don't have a soy allergy, or a tendency to drink 3 quarts of soy milk a day!

Keep in mind that maintaining a healthy weight, exercising, managing stress, and having a balanced gut microbiome also play important roles in supporting optimal hormone levels.

The other concern with soy is that it is one of the most widespread GMO crops, however, the GMO soy is mostly used to feed farm animals, and if you choose organic soy then it is non-GMO. Also, similar to other beans, soy can be difficult to digest for some people. Choosing fermented (tempeh, miso) and sprouted options will help increase digestibility.

If you are interested in learning more, here are some great resources:

How Much Soy is Too Much? - more than 5 servings/day increases IGF-1 almost as much as meat consumption. Higher circulating levels of IGF-1 increases the risk of certain cancers. Note that the risks from excessive intakes of soy are not to do with estrogenic effects.

Interested in learning what you can do to support optimal hormone balance?​Book your complimentary 15 Min Discovery Call to discuss how Private Nutrition Coaching or a Custom Meal Plan can help you will reaching your health goals.